This invention relates generally to radiation sensing detectors and more particularly to detectors producing plural electrical outputs in response to impinging radiation at distinctly different wavelengths.
The use of epitaxial semiconductors as infrared detectors in a multi-color imaging system, is generally well known. In such prior detector arrangements, photovoltages are developed across separate junctions respectively formed on the semiconductors having different bandgaps and on which separate optically active surfaces are established in order to achieve multi-color operation. Since each junction responds to only a spatial portion of the incident optical input, there is a loss of signal content. Further, when such detectors are arranged in an array configuration signal loss is especially severe because of non-coincident radiation focussed on separate areas at different times.
The use of two radiation absorbing layers of a photosensing device that are stacked in alignment with a common axis of coincident impinging radiation to respectively absorb different components of such radiation at different wavelengths, is disclosed in U.S. Pat. No. 4,651,001 to Harada et al. One of such layers is made of amorphous silicon according to the Harada et al. patent to sense only a visible wavelength component of input imaging light while the other radiation absorbing layer formed on a substrate is made of a photovoltaic platinum-silicon compound to absorb only an infrared component of light within a totally different spectral range. Obviously, the arrangement disclosed in the Harada et al. patent is incapable of, and not designed to, separately sense mutually exclusive components of radiation at different wavelengths within the same spectral range.